1. Field of the Invention
The present invention relates to a key switch device provided with, between a key top and a base plate, a guide support member for guiding the vertical movement of the key top, the guide support member being constructed of two link members rotatably coupled in an intersecting configuration. More particularly, the present invention relates to a key switch device capable of effectively utilizing the thickness of the base plate such that a processing quantity for an engagement portion for engaging the link members with respect to the base plate can be reduced to thereby achieve a low-profile key switch device.
The present invention also relates to a key switch device capable of increasing a keystroke quantity while keeping a low-profile of the key switch device.
2. Description of Related Art
Conventionally, there have been proposed key switch devices provided with a key top having two pairs of engagement portions which are formed at four corners of a back surface of the key top, a base plate made of a thin metal plate having two pairs of engagement portions corresponding to the key top engagement portions, and a guide support member disposed between the key top and the base plate. The guide support member is constructed of two link members that are coupled in an intersecting configuration These intersecting link members are connected to the key top and the base plate respectively through the engagement portions.
A basic structure of the conventional key switch device of this type is explained below referring to FIG. 17. FIG. 17 is a cross sectional side view of the conventional key switch device.
In FIG. 17, a key switch device 100 is mainly constructed of a key top 101, a guide support member 102, and a base plate 103 which is a thin metal plate made of, for example, aluminum.
On a back surface of the key top 101, first engagement portions 104 having a circular hole and second engagement portions 105 having a slot are arranged respectively in pairs. It is to be noted that only one of the first engagement portions 104 is shown in FIG. 17 and the same applies to the second engagement portions 105. The guide support member 102 for guiding a vertical movement of the key top 101 is constructed by two link members 106 and 107 which are mutually rotatably coupled in an intersecting configuration at an axial support part 108. The link member 106 is provided with engagement pins 109 and 110. The link member 107 is provided with engagement pins 111 and 112. On the base plate 103, third engagement portions 113 are formed at positions corresponding to the first engagement portions 104 of the key top 101 by a drawing process. Similarly, fourth engagement portions 114 are formed at positions corresponding to the second engagement portions 105 of the key top 101 by a drawing process.
The pin 109 formed on the link member 106 at its upper end is rotatably engaged in the first engagement portion 104 of the key top 101. The pin 110 formed on the link member 106 at its lower end is slidably engaged in the fourth engagement portion 114 of the base plate 103. The pin 111 formed on the link member 107 at its upper end is slidably engaged in the second engagement portion 105 of the key top 101. The pin 112 formed on the link member 107 at its lower end is rotatably engaged in the third engagement portion 113 of the base plate 103. A rubber spring 115 provided with a movable electrode (not shown) on an inner upper wall is disposed between the third and fourth engagement portions 113 and 114 on the base plate 103. Above the rubber spring 115, an axial support part 108 of the guide support member 102 is placed.
The key switch device 100 constructed as above is operated in the following manner. When the key top 101 is depressed, as shown in FIG. 19, the key top 101 is guided downward maintaining its horizontal state through the guide support member 102, and then the rubber spring 115 is buckled by the axial support part 108. Then, the movable electrode of the rubber spring 115 carries out a predetermined switching operation in cooperation with a switching circuit (not shown) provided on the base plate 103.
In the conventional key switch device 100, as shown in FIG. 17, the following distances are set to be equal; a distance L1 between the upper pin 109 of the link member 106 and the axial support part 108; a distance L2 between the lower pin 110 and the axial support part 108; a distance L3 between the upper pin 111 of the link member 107 and the axial support part 108; and a distance L4 between the lower pin 112 and the axial support part 108.
Meanwhile, the base plate 103 used in the key switch 100 is formed of a thin aluminum plate for rust prevention and reduction in weight. The third and fourth engagement portions 113 and 114 are formed by drawing a part of the thin aluminum plate.
The aluminum itself in metal material that is not expansible, though it is suitable for the purposes such as rust prevention and weight reduction. Thus, the third and fourth engagement portions 113 and 114 formed by a drawing process may easily be cut or broken at an upper portion during the drawing process. If the upper portions are cut or broken, the third and fourth engagement portions 113 and 114 can not support the rotation of the pin 112 and the slide of the pin 110, which interferes a smooth operation of the key top 101.
The pin 110 of the link member 106 and the pin 112 of the link member 107 are placed on the upper surface of the base plate 103 so as to be slidably or rotatably in the third engagement portion 113 or the fourth engagement portion 114 of the base plate 103. Here, explanation is made on one example of a relationship between the pin 112 engaged in the third engagement portion 113 and the base plate 103, referring to FIG. 18. FIG. 18 is a schematic explanatory view of the engagement relation of the pin 112 with the third engagement portion 113 of the base plate 103 in the conventional key switch, device 100; FIG. 18(a) is a perspective partial view of the pin 112 engaged in the third engagement portion 113; and FIG. 18(b) is a sectional view of FIG. 18(a).
In FIGS. 18(a) and 18(b), the pin 112 of the link member 107 is rotatably engaged in the third engagement portion 113, when the lower surface of the third engagement portion 113 and the upper surface of the base plate 103 rotatably support the pin 112 and restrict the rotation of the pin 112. In this state, the pin 112 is placed on the base plate 103 as shown in FIGS. 18(a) and (b).
Since the pin 112 is disposed on and supported by the upper surface of the base plate 103 as mentioned above, when the drawing quantity of the third engagement portion 113 is not set to be larger than a given processing quantity, the third engagement portion 113 can not properly hold the engagement pin 112 so as to be rotatable. Accordingly, it is impossible to reduce the processing quantity from a viewpoint of a drawing process for the third engagement portion 113.
Since the pin 112 is disposed on the upper surface of the base plate 103, the height of the key switch 100 would increase in proportion to at least the thickness of the base plate 103. Due to this, it is difficult to satisfy a current request to promote the thinning of a key switch device.
Furthermore, the tendency to reduce the height of the key switch device 100 constituting a key board attached to note type personal computers and note type word processors increases year by year. This thinning tendency can be accomplished by thinning the key top 101 itself.
However, when the key top 101 is formed a thin shape in response to the tendency of a thin key switch device, the key top 101 may be deformed due to its reduced thickness. Such the deformation would provide a bad appearance. In addition, it becomes more difficult to ensure keystroke as the key switch device 100 is further thinned. This deteriorates key operability.